While easily achieved in electric cooktops, simmer temperatures have until now been complicated issues for gas cooking apparatus. Conventional gas cooktops are generally operated by using manually activated mechanical actuator knobs, with infinitely varying settings of the flow of gas by rotating associated gas proportional valves. Most often, adjustment of cooking level is achieved by comparing level indicators printed on the knob, to a fixed pointer printed on the cooktop surface, immediately surrounding the knob. With such knobs and associated infinite valves, it often becomes difficult for the user to precisely re-adjust the valve to a predetermined preferred level of BTU output and thus repeatability is rarely achieved. This effect is of an even greater concern in simmer mode of cooking where delicate food such as chocolate or sauces can be spoiled, if cooked at slightly higher temperatures than those recommended. Additionally, mechanical knobs are also usually susceptible to wear and tear and are often vulnerable to contaminants normally present in cooking areas, such as greases and moisture infiltration that generally find their way through open areas, necessary for the mechanical valve installation in the cooking surface. Spark igniters are typically used to ensure ignition of the gas and are generally activated upon rotation of the above-mentioned mechanical knobs. Most often, integrated sensors, such as flame detectors, are used to continuously monitor proper combustion of the gas. Such sensors typically provide feedback to the spark ignition module, to ensure re-ignition of the gas, should it fail to combust. However, very low flames have been proven hard to detect by such sensor types and are often a cause for spark igniters to unnecessarily generate discharges in response to false detection incidents. Spark igniters are also known, by those in the industry, to emit powerful electromagnetic interference (EMI) that often disturbs electronic equipment working in their vicinity. Microcontrollers used in electronic controls are also known to be highly susceptible to EMI emission, and hence generally need additional protection when used in conjunction with spark igniter modules in gas cooking apparatuses. Due to their large orifice size, burners that are capable of high BTU output are usually not suitable for simmer, one of the reasons being that smaller flames have the tendency to self-extinguish in such conditions. Therefore, some cooktops have been equipped with simmer burners, featuring smaller orifice diameters and capable of delivering stable low-to-medium BTU output. This has often had the effect of reducing the number of available burners capable of high BTU output on a given cooking surface. Various methods involving flame sequencing have been used to provide gas-cooking appliances with low temperature output to provide a simmer. Sequencing the flame on and off in a timely fashion provides for an elegant solution to achieve very low is BTU output from a burner also capable of high BTU output, but simmer systems of the prior art generally involve synchronized re-ignition of the gas following each flame on/off cycle, complicating even further the design of simmer controls in gas cooktops. Moreover, repeated re-ignitions of the gas during simmer mode often have the undesirable effect of continuously generating harmful electromagnetic interference. As mechanical valves are traditionally used to adjust the gas flow, additional electrically controlled “on/off” cycling solenoid valves are generally added to provide the “on/off” sequencing of the flame in simmer mode, contributing to higher system cost and reliability issues.
U.S. Pat. No. 4,376,626 to Rossi et al. (Device for the control of a sequential burner of a cooking apparatus) discloses a control device for at least one sequential burner of a cooking apparatus, comprising in combination: a geared-down synchronous motor and a drum which can be driven in rotation by this motor, an electric circuit associated with this drum, comprising at least one electric contact pressing upon the surface of the drum and at least one electrically conductive track arranged on the drum in such manner as to permit operation of the burner according to heating sequences which are variable as a function of the position of the electric contact on the drum, and means for adjusting the position of the contact in relation to the conductive track in order that the duration of the heating sequences of the burner may be varied progressively and continuously.
U.S. Pat. No. 5,575,638 to Witham et al. (Stove burner simmer control) discloses a burner control which provides a pulsed flame sequence in response to a user's selective manipulation of an actuator through a range of response. A microcontroller-based control module switches both a burner igniter control and an electric valve for gas supply to the burner in a predetermined time sequence depending upon the actuator position within the predetermined range. Preferably, one or more of a plurality of burners on a single cooking top are controlled for pulsed sequence operation, and a single actuator for each channel, preferably in a form of a rotary knob, provides a simple user interface for utilizing the pulsed flame sequence, preferably in a low gas flow or simmer cooking range.
U.S. Pat. No. 6,116,230 to Clifford et al. discloses a gas appliance comprising a burner, a conduit, a control circuit, and a valve. The control circuit is adapted to provide a pulse-width-modulated signal to the valve, whereby the valve provides a substantially linear flow rate of fuel from a fuel source to the burner. The gas appliance of Clifford et al. employs a spark igniter.
Thus, there is a need for an electronically controlled gas cooktop appliance capable of delivering true simmer temperatures from gas burners that are also capable of high BTU output. There is also a need for an electronic gas cooktop appliance that is capable of fine, precise, and repeatable control of heating levels, provided by a direct level-dialing control, thus providing the user with a more precise selection of available and controllable temperatures. There is also a need for a gas cooktop appliance capable of assuring flame re-ignition without generating harmful electromagnetic interference. There is equally a need for a gas cooktop flame-sequencing simmer system integrating gas-flow modulation and “on/off” sequencing ability into a single gas valve. Finally, there is a need for a gas cooktop appliance integrating an electronic user touch interface for burner activation and selection of temperature settings.